| Along with the requirement for scientific research and the rapid development of computer technology,the theoretical calculation has been applied extensively in chemistry and biology,which provides an effective method to research material structure,intermolecular interaction and chemical reactions at the microscopic scale,and compensates the limitations from experimental.In this work,the quantum chemical calculations are applied to explore the influence of intermolecular interactions on the nuclear magnetic parameters in nucleic acid bases,also the influence of zeolite pore confinement effect on the stability of adsorbates and reaction activity,and some meaningful results are obtained.1.A theoretical investigation of 17 O nuclear magnetic parameters influenced by intermolecular interactions in nucleic acid bases.We theoretically built a series of nucleic acid bases(thymine,uracil,cytosine and guanine)models with different dimension size,and investigated the chemical shift and quadrupole coupling constant(Qcc)of 17 O.The periodic model was also considered in order to elucidate the impact of the surrounding environment.Based on the calculational results and further comparison with the experimental data,it is found that the calculated values are in good agreement with the experimental results only when the intermolecular interactions was considered as much as possible.By combining the charge variation of carbon and oxygen atoms and charge density difference analysis,demonstrates that the charge transfer from carbonyl carbon atoms to oxygen atoms leads to the chemical shift of 17 O to high magnetic field,especially in the periodic model.2.Using energy decomposition analysis(EDA)method explores the zeolite pore confinement effect.Besides the acid properties of zeolite,pore confinement effect has received extensive attentions from research workers due to its great influence on activities of acid-catalyzed reactions.Based on the quantitative characterization of EDA method,we systematically studied the stabilization mechanism of alkene,alkoxy species and carbenium ions intermediates confined inside ZSM-5 and BEA zeolite.It was demonstrated that for neutral alkene,the dispersion interaction plays a key role in their stabilization.In addition,both dispersion and repulsion interaction will be strengthen with the increase of adsorbed molecular size,in this case,the bulky adsorbate will be unstable due to the dramatic steric repulsion.For carbenium ion intermediates,the electrostatic interaction favors their stabilization based on their significant charge characteristics.Alkoxy complex is covalently bound to the zeolite framework,in which not only the charge transfer but also part of the orbital overlap occurs,so that their stability is determined by both electrostatic and orbital interactions.3.Theoretical study of olefin protonation reactions influenced by zeolite pore property using EDA method.The protonation reaction is important elementary step in the petrochemical industry,such as dimerization,oligomerization of olefins and the formation of hydrocarbon pool species in the MTO conversion.The influence of both Br?nsted acid strength and pore confinement effect on olefin protonation reactions has been systematically studied by density functional theory(DFT)calculation.Compared to ethene and isobutene,the size of propene is comparable to the pore size of 8-membered ring(8-MR),in this case,a high reactivity was observed based on the dramatic confinement effect.While in the large 12-MR channel,confinement effect has little impart on these adsorbates,the protonation reaction is improved with their basicity enhanced from ethene to isobutene.On the basis of calculated energy,it is found that the host-guest interactions act as the key factor in determining the activation barriers in contrast to the strain energy of adsorbates and zeolite framework.The further analysis for the transition states(TS)by EDA method,it is demonstrated that their stability mainly depends on electrostatic and orbital interactions. |
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